Screened positive for use in preparation of intaglio printing plates and method of making said positive



May 13, 1952 L. c. AUSTIN 6, SCREENED POSITIVE FOR USE IN PREPA ION OFINTAGLIO PRINTING PLATES AND METHOD OF MAK SAID POSITIVES Filed Dec. 26,5

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SCREENED POSITIVE USE I REPARATION OF INTAGLIO PRINTING PLATES ANDMETHOD MAKING SAID POSITIVES Filed Dec. 26, 1945 2 SHEETS-SHEET 2 5 r-F915 5 57 55 lK/OZAET I 0 g 55 55\ 7E F19 Z5 F1911 F914- INVENTOR.

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ATTOR/VEKS Patented May 13, 1952 UNITED STATES PATENT OFFICE SCREENEDPOSITIVE FOR USE IN PREPARA- TION OF INTAGLIO PRINTING PLATES AND METHODOF MAKING SAID POSITIVE 4 Claims. 1

My present invention relates to intaglio or gravure printing forms, andto methods and apparatus for producing the same. More particularly myinvention relates to improved photogravure printing forms adapted formodern high speed long run printing operations, which may be producedwith less skill than the prior forms, and which provide prints of bettertone and color value than it is possible to produce with the priorphoto-gravure processes commonly used in high speed commercial printingoperation.

As is well known, in the usual type of rotogravure printing positiveshave a tonal range of from about .3 to 1.6 by densitometer reading. Thusalthough these readings fall short of a full range as applied tophoto-engraving or photolithography the nature of the next step in theprocess of gravure pigment paper or carbon tissue results in theproduction of etchings or printing forms full scale screen formation isutilized in which the ink is retained in substantially square wells orpockets of uniform area each separated from the adjacent wells by thinmetal walls, the outer surfaces of which support and are wiped free ofink by the doctor blade of the press in printing operation. In suchforms the walls of the wells are etched at an angle of approximately 45degrees to the wiping edge of the doctor blade which is parallel to theaxis of rotation of the printing cylinder or form. The varying tones ofthe print are secured by etching the ink receiving wells to differingdepths, with barely perceptible wells in the absolute high light areas,and wells increasing in depth from the high light to the deepest shadowareas. The constant rubbing or wiping of the doctor blade against theflush outer surfaces on such etchings results in friction and wear,which, particularly at higher printing speeds and in long printing runs,may make replacement of worn cylinders or forms necessary beforecompletion of the run, with no certainty that the etched replacementcylinder or form will conform with sufficient accuracy to the initialform, particularly in color work where accurate registration andduplication of tone values of the different color etchings is essentialfor satisfactory printing.

A further difficulty in the use of the prior rotogravure printing formsis that the individual etched wells are substantially U-shaped, and ifthe etching is not carefully done the etching fluids undercut the welloutlet periphery. As a result the full complement of ink is never drawnfrom either of these well shapes in the printing operations. This attimes requires excessive depth of etching to secure reasonablysatisfactory prints at commercial printing speeds and results in loss oftone values in the dots due to the fact that the ink deposited on theprint is not accurately controlled by the well size and shape.

As the speed of printing is increased with such etchings, the quality ofthe print progressively deteriorates, particularly when modern highspeed quick drying inks and ink fountains are used. This is due to thetendency of the ink to pull out of the cells under the wiping action ofthe doctor blade, and to the diminishing quantities of ink withdrawnfrom the wells as the printing speeds are increased. This results infurther destruction of print tonal values and limits the printing speedof the usual rotogravure process.

In efforts to overcome the foregoing difficulties encountered in highspeed long run printing with the usual rotogravure printing forms andmethods, several printing forms have been developed in which tonevariations are secured by etching separated substantially square inkreceiving pockets or wells of varying areas, essentially U-shaped insection and substantially uniform depth in general checkerboard patternso as to deposit dots of ink of varying size on the printed surface. Thetone differences are secured with such etching by depositing the largestdots in the shadow areas and the smallest dots in the high light areasof the print. The checkerboard pattern is particularly evident in themiddle and lighter tones in which the substantially square wells are.separated by substantially square unetched metal surface areas. Suchetchings are commonly referred to as dot-size etchings.

They are formed by use of screen positives made by suitable exposure ofa full tone negative of the subject through a half tone screen, andembody a short scale screen formation in checkerboard arrangement due tothe effects of light diffraction by the screen. In a full scale screenformation the space between the dots is a minimum in the shadow tones,while in a short scale screen formation the space between the dots islarger and the dots are correspondingly smaller in the shadow tones.Because of their checkerboard pattern, and variation in dot sizes toprovide tonal effects, they have substantially greater metal areasbetween the printing wells for the support of the doctor blade, andaccordingly provide more durable printing surfaces than the fully etchedscreen formation gravure etchings. The short scale screen formationincreases the tendency to print the screen pattern, and this also givesespecially in the shadow tones a lack of distinct tonal values in dotsonly slightly different in size due to the large non-printing metalsurface areas which prevents satisfactory printing in modern high speedrotogravure presses due to excessive loss of tone values in the print.

To overcome the foregoing deficiency of the dot-size forms in high speedprinting, etched printing forms have been developed which, in additionto the checkerboard pattern, and variations in area of the ink receivingwells of the dot-size forms, embody variations in depth of the wells toadd improved tonal value over the dot-size etchings. This form ofetching has gone into successful use in multi-color high speed long runrotogravure printing. Such forms are commonly known as dot-sizedot-depth etchings and are successfully used in the commercialmulti-color rotogravure printing for long runs on modern high-speedpresses. Like the dot-size etchings, the dot-size dot-depth etchingsembody short scale screen formation and U-shaped wells which lackseparate and distinct tonal values and form literally half tone images,the shadow tones starting a little below the middle of the regularscreen plate scale.

The dot-size dot-depth process provides no improved printing values atlow speed over the usual photo-gravure process and is therefore usedonly for high speed color printing. Both the dot-size and dot-depthetchings have so much non-printing area that lack of tone in the printsis evident at high printing speeds. While the dot-size dot-depthetchings provide about 25% more tone scalethan the dot-size etchings,the dot-size dot-depth prints fall short of the full tone scale attainedin the usual rotogravure process, and even the dot-size dot-depthetchings are therefore useful only for high speed color work.

The regular gravure process provides the longest period for properlycompleting the etching and thus provides a maximum degree of control.This period is from about twenty-five to thirty minutes. The dot-sizeprocesses provide the shortest etching period of from about three tonine minutes, giving the least control of the etching. The dot-sizedot-depth etching period, and consequently the control provided, isintermediate the regular gravure and dot-size processes, and extendsfrom about eleven to fourteen minutes.

To produce commercially acceptable prints by any of the foregoingprocesses requires considerable skill in the various stages ofpreparation of the printing surface including considerable retouching,much of which is done on the positive image and will often increase from1.7 to 2.5 the densitometer reading of a good regular rotogravurepositive. And when the positive is retouched it loses its value ofstandard density range for the subsequent workers.

The normal process of rotogravure requires use of a pigment paper printfrom a common gravure screen at forty-five degrees for monotone work. Inusual rotogravure multi-color printing adifferent screen angle is usedfor at least the three darker of the four colors, to effect a slightrelative displacement of the deposited color dots on the print andprevent moire screen formation on the composite print.

The dot-size dot-depth process in use for color work requires thespecial skill of very well trained above average workers previouslyexperienced in the production of the usual rotogravure multicoloretchings and photo-engravings. To produce such etchings requires use ofscreen positives with the shadow tones starting a little below themiddle of the usual screen plate scale. To correct color deficienciesand to extend the short scale screen positive, continuous tone positivesare used in conjunction with the screen positive which must be underscale photographically compared to the usual gravure continuous tonepositive. These are in turn over-retouched to correct photo-colordefects and also defects due to lack of scale in the screen half-tonepositive. The retouching on some of the continuous tone positives forthis method often extend up to opacity the limit of the densitometerreading, to give the fullest possible effect in correction of tonevalues for etching in what is literally only a half-tone process.

A primary object of my present invention is accordingly to provide animproved intaglio printing form of the dot-size dot-depth type in whichthe advantages of improved full scale screen coverage area formationplus the softness of tone range of the best kind of continuous tonepositive for producing the finest regular roto gravure etching, withimproved tone values in the prints, are secured and the foregoingdisadvantages of the prior photogravure etchings are minimized oreliminated.

A further object of my invention is to provide improved intaglio orgravure etchings, and processes of and apparatus for producing the same,whereby higher quality gravure prints are produced in longer commercialhigh speed runs.

A further object of my invention is to provide novel intaglio etchingshaving separated minute ink receiving wells of varying size and depth,depending upon the tone values, and in which the individual wells havetheir maximum areas at the printing surface of the etching and decreasein area from the surface inward in a manner permitting complete removalof all of the ink from each printing well during each printing operationregardless of the nature or consistency of the ink. This providesseparate and distinct tone values and each different size of dot withtonal values and quality of print not heretofore obtainable with anyprior photo-gravure etching. With my improved etching it is possible toreproduce the deepest shadow of a subject with shadow detail the finesthigh-light tones and detail, in modern high speed printing operation ina manner not heretofore attainable.

A still further object of my invention is to provide an improved dotshape dot size and depth process which is substantially like regularrotogravure etching in procedure, but in which tonal control of thepositive dots is secured through shaping of the etched cavities, notattainable in any other known intaglio screen process.

Another object of my invention is the provision of processes andapparatus for the production of improved dot-size dot-depth screenpositives in which each size of dot, from the deepest shadow to thefinest highlight has a separate and distinct tone value.

A further object of my invention is the provision of a dot-size screenpositive in which each dot has a central core of maximum density anddecreases in density to the periphery of each dot, and in'which the dotsare of substantially square full scale screen formation, rather than theusual dot-size checkerboard dot arrangement.

Still another object of my invention is the provision of a novel screenpositive of a subject in which the image is made up of separate dotswhich vary in size to impart tonal values to the image with the largestdots in the deep shadow tones and the smallest dots in the highlighttones, and in which each dot increases in density from its periphery toa central core, and each dot from the deepest shadow dot to the smallesthighlight dot diminishes in tone value as it diminishes in size.

A further object of my invention is to provide an improved photographicscreen positive comprising dots of differing sizes and tonal valuesseparated by transparent areas in which the tonal values. increase froma minimum in the highlight tones to a maximum in the deepest shadowtones, and having the tonal range of a regular rotogravure positive asestablished by densitometer readings.

In the prior processes color correction is necessarily made byretouching the positive used to produce the etched surface. Thisprocedure is subject to uncontrollable variations due to the humanequation introduced, and is the definite cause of lack of ability tostandardize the etchings produced. Another object of my invention is theprovision of improved screen positives for the production ofphotogravure etchings which need not be retouched for printing and cantherefore be made standard in tone reading, and for the first timepermit the use of predetermined etching acid formulae to providepredetermined tones in the prints, thus enabling uniform high gradeetchings and resulting high grade prints to be secured with workershaving considerably less skill than at present required for any of theknown photogravure processes.

A still further object of my invention is the provision of improvedcamera screen and stop arrangements and novel methods of utilizing thesame in the production of improved high grade photogravure screenpositives with a minimum use of skilled workers.

Still further objects of my invention will appear from the followingdetailed description of the preferred embodiments thereof and from thescope of the appended claims. As shown in the drawings:

Figure 1 is an enlarged diagrammatic illustration of a tone scale.

Figure 2 is an enlarged fragmental diagrammatic illustration of a usualtype of rotogravure screen;

Figures 3 and 4 are fragmentary diagrammatic sectional and plan viewsillustrating in enlarged size the shape of the ink receiving wells in anetched photogravure cylinder or printing form of the usual type;

Figures 5 and 6 are fragmentary diagrammatic sectional and plan viewsillustrating in enlarged size the ink receiving wells of a prior dotsizeetched photogravure cylinder or printing plate resulting from practiceof the process of U. S. Patent to Stirling, Number 1,773,887.

Figures 7 and 8 are similar fragmentary diagrammatic sectional and planillustrations of a prior dot-size dot-depth photo-engraved printingcylinder or plate resulting from practice of the process of DultgenPatent No. 2,096,794;

Figure 7A is a diagrammatic sectional view of the plate of Figure 8 infinal form;

Figures 9 and 10 are similar diagrammatic fragmentary sectional and planviews of an improved corona tone dot photo-engraved printing form of thepresent invention;

Figure 11 is a diagrammatic illustration of a preferred camera, stop,and screen arrangement for producing the screen positive used in etchingmy improved corona tone dot printing form or plate of the characterillustrated in Figures 9 and 10;

Figure 12 is an illustration of a usual form of stop used in producingdot-size screen positives;

Figures 13, 14 and 15 are illustrations of preferred forms of stopsutilized in producing the improved corona tone dot negative of mypresent invention;

Figures 16 and 17 are fragmental diagrammatic illustrations of screenformations used in producing my improved screen positive.

Figure 18 is an illustration of the completed dot formation of myimproved screen ,positive.

Figures 19, 20 and 21 are illustrations of the effects of the exposureswith the stops shown in Figures 13, 15 and 14 respectively.

In Figure 1, I have illustrated as a subject for each of the etchingshereinafter described, a tone scale embodying a deep shadow area 22, amedium tone area 23, a highlight area 24 and an absolute highlight area25.

In etching the regular rotogravure printing form an image of the usualscreen 26 (Figure 2) is first printed on the sensitized pigment resist.Such a screen consists of uniform opaque square dots 27 separated bytransparent line areas 28, the ratio of the line spare area to the dotarea generally being about 3 to 1. A positive of the subject (forexample the tone scale of Figure 1) is then printed on the screenexposed resist, the exposed resist is then transferred to the cylinderor form and developed and the cylinder is then etched in Well knownmanner.

As illustrated in Figures 3 and 4 the usual photogravure etching orprinting form 29 formed in this way includes a series of ink receivingpockets or wells 30, 3|, 32 and 33 having substantially square surfaceopenings separated by thin substantially uniform walls of metal, usuallycopper, which in monotone printing are generally at an angle of 45degrees to the wiping edge of the press doctor blade (not shown) whichin turn is parallel to the axis of rotation of the etched cylinder inthe usual rotogravure press. Wells 38 are the deepest, receive a maximumamount of ink and, print the deep shadow tones of the subject. Wells 3|are of medium depth, receive less ink, and print the medium tones. Wells32 which are very shallow, print the highlight tones. Wells 33 arebarely perceptible and print the absolute highlights.

The acid etches the wells into the copper in substantially U-shapedsection, and the openings of the well are squares of substantially equalarea surrounded by very thin relatively narrow outer metal wall whichtend to wear away relatively rapidly under the friction of the doctorblade. This alters the nature of the prints and may require replacementof etchings in long runs. As is well known, it is very difiicult to makereplacement etchings exact reproductions of the original etchings.

Also because of the U-shaped section of the wells the full complement ofink is never drawn from the wells in the printing operations withresultant loss of tone. value differences in wells of slightly differingetched depths. Furthermore the amount of ink withdrawn from such wellsin successive prints depends largely on the ink consistency which variesmaterially in modern high speed inks. Relatively deep etched Wells aretherefore necessary to secure reasonably satisfactory prints atcommercial printing speeds, and relatively full tone print values of thesubject are secured only in comparatively slow sheet feed presses withsuch etchings. As the speed of rotogravure printing is increased withsuch etchings, the action of impression roll at high speed plus thetendency of the doctor blade to draw ink from the wells result indecreasing quantities of ink drawn from the wells by the web and rapiddeterioration of the prints.

In the dot size etching a form 34 shown in Figures and 6 the sensitizedresist is subject to a single exposure from a. screen positive on whichan image of the subject is formed by dots of varying size. An etching 34formed by use of such a positive and resist has wells 35, 36, 31 and 38,which are of undercut U-shaped in section as shown in Figure 5 due tothe forced nature of the etching. In this form of etching as shown inFigure 5, the well openings are substantially square except where thetonal Values change in a given cell as illustrated at 35a, and are incheckerboard formation, with their sides at approximately forty-fivedegrees to the edge of the doctor blade. These wells decrease in areafrom the shadow tone area of wells 35 through the medium tone area ofwells 36 to the highlight tone areas of wells 31, with very small wells38 or no wells at all in the absolute highlight areas. While thevariation in dot sizes and the half tone checkerboard or short scalescreen arrangement provides greater metal areas between the printingwells for the support of the doctor blade, resulting in more durableprinting surfaces than are provided in the usual rotogravure etchings ofFigures 1 and 2, the short scale screen formation used and the undercutwell formation prevents satisfactory printing in modern high speedpresses, due to excessive loss of tone values and the tendency toreproduce the checkerboard pattern in the middle and light tones of theprints as the printing speeds are increased above the speeds of sheetfeed presses.

In preparing the dot-size dot-depth etching 39 of Figures 7 and 8, adot-size screen positive is first printed on the sensitized carbontissue as in the dot-size process. A continuous tone positive retouchedto give varying depth from any given size dot of the screen positive isthen printed over the dot-size image to increase the tonal differencesin the individual dots. The exposed carbon tissue is then transferred tothe printing form, developed and etched into the printing surface. Insuch an etching, the wells 40, 4|, 42, and 43 decrease in area as in thedot-size etching of Figures 5 and 6, from the deep shadow tones 40through the medium tones 4|, the highlight tones 42 and the absolutehighlights 43. It will be noted that the depths of the wells differ withthe areas of the wells, and that in each tone two well depths have beenillustrated. The shallower of the wells in each tone illustrates theholdback effect of the continuous tone positive in producing theetching, and the deeper illustrates the well formations when producedwithout use of a continuous tone positive in the etching operation. Thefinal plate embodying dots varying in size and depth is shown in Figure7A. The wells in each case are substantially U-shaped and vary in depthin accordance with the tonal values, as shown in Figure 7, the deepshadow tone wells 40 being the deepest. The well depths decreaseprogressively from the corrected and uncorrected deep shadow tone wellsthrough the medium tone wells 4 I, the highlight tone area of wells 42,to a minimum depth in wells 43 of the absolute highlight tones. facearea for support of the doctor blade increases their life over that ofthe usual rotogravure etchings, and provide about 25% more tone scalethan the dot-size etchings due to the depth variations of the wells, theprints fall short of the tone scale attained in the usual rotogravureprocess, and are useful only for high speed medium grade color work.

My improved printing form 44 (Figures 9 and 10) of the present inventionis etched from a novel screen positive of the subject carrying the tonevalues of the regular rotogravure positive and made as hereinafter morefully set forth. The image on my improved screen positive is formed ofsubstantially square dots of varying size and as more fully hereinafterset forth each dot increases in density or resistance to thetransmission of light from its periphery to a central core for motion ofmaximum density, and each dot from the deepest shadow dot to thesmallest highlight dot diminishes in tone value as it diminishes insize. The phrase motion of maximum density has been coined by me todescribe the novel growth of the dots and etched cavities or wells inthe practice of my invention. The dots are formed by successiveexposures causing them to form with varying density, and the etchedcavities or wells grow from a pin point core and increase in area asthey increase in depth, producing density in printing value. My screenpositive is printed on a carbon or pigment resist which is transferredto the printing form, then developed and etched in usual manner. Theresulting etching illustrated in Figures 9 and 10, as in the dot-sizeetchings decrease in area from a maximum in the shadow single tone wells45 through the shadow two tone wells 45a, the medium tones wells 45 thehighlight tone wells 41, to a minimum in the absolute highlight wells48. In exceptional cases where absolute whites are desired in thehigh-light tones, absolute high-light tonal values which will produce nodots are created in the negative used as a transparency to produce thepositive. In some instances this is procured by the nature of the groundof the copy, and in others it is secured by correction of the negative,all in manner well known to those skilled in the art. The crosssectionalshape of each of the wells 45 through 48 is furthermore substantiallytapering V- shaped from a maximum at the surface openings of the wellsto a minimum at the bottoms. This results in inclined supporting sidesfor the surface sections adjacent the wells providing improvedresistance to the 'doctor blade pressures and frictional wear. Theinclination of the well walls of my improved etchings is such that allof the ink is readily drawn from each well for each print under modernhigh speed printing conditions with normal ink variations. As a resulteach different size of well, no matter how minute the differences insize, deposits a differ ing individual amount of ink on the print. Eachdot from the deepest shadow dot to the smallest absolute highlight dottherefore deposits a distinctive individual tone of dot, providing tonevariations not heretofore obtainable in any prior type of photogravureetching when used for high speed printing.

In producing my improved screen positive I may use a camera of the usualhalf-tone type. I prefer however to use a camera of the type While thelarger sur- 54 preferably a diffusing plate.

of the negative is interposed between plate 54 and optical prism '6which mounted above and in the path of the light projected through thenegative. Prism 56, is provided with an exposure shutter 51 operated byrod 51a from the back of the camera in well known manner, and issupported on the end of lens barrel 58. ported in lens barrel 58 is lens59. The outer end of the lens barrel and the upper part of light shield55 are supported by a member 60 from the camera body El. Mounted inbarrel 58 is a rotatable stop frame 52, and the barrel is secured at itsinner end to and extends slightly into a camera body 6!, which at itsrear carries a plate or film holding camera back 63.

Mounted rotatably in body BI is a truncated conical tube 64 the forwardwall of which is; journalled on the inner end of. lens barrel 58,

adjacent its ends tube 64 is rotatably supported in cradles 55. Mountedon the rear end of tube 64 is a screen supporting frame 66. Tube 64 isconnected by an extension 61 passing through a suitable slot in thefront wall of body 6| to the stop carrying frame 52. By thisconstruction the screen assembly and stop are held in predeterminedlongitudinal relationship with respect to each other, the lens assemblyand the.

3 for the passage of light mounted in stop;

frame 62 a checkerboard screen pattern of separated dots of the typethat will produce the dot formation of Figures 6 and 8 is projected onthe sensitive surface. These dots decrease in size from a maximum in thedeepest shadow;

tones to a minimum or no dots at all in the absolute high light areas. IHowever, by use of a series of different stops, such for example of theshapes illustrated in Figures l3, l4 and 15 inserted in stop frame 62 insuccessive exp0-' sures, I modify the checkerboard screen formation intoa full scale screen formation of the inafter described.

For best results I prefer to use a normal or' continuous tone rathersoft emulsion plate or film, which cannot be used for the usual halftone screen work, because they will not provide a sharp clot formationof the half tone process plates, due .to their softness. Such normal orsoft emulsion plates are used in my improved process because very littlelight will cause reaction on the plate and create an image. On the otherhand, the prior dot-size processes require a very contrasty plate whichemphasizes the dot image with respect to the clear plate areas, andrequire a full complement of light during exposure.

I preferably interpose between objective screen I H and the sensitizedplate or film 14 mounted in back 53, preferably held in place bysuction,

10 a secondary screen 15 (Figures 11 and 17) disposed directly againstthe sensitized surface, with its screen lines and transparent or lighttransmitting square openings respectively in register or opticalalignment with the lines and openings of the primary or objective screen'il so that a single screen image is projected on the sensitizedsurface. By way of example, with a 150 line 60 to 40 ratio objective orprimary screen H as above described I have used a 150 line to 20 ratioof openings to rulings in the secondary screen 15. As will be understoodby those skilled in the art the relative screen rulings and spacings maybe varied widely depending upon the lenses and camera extension used andthe screen positive effects desired. The secondary screen 15, when used,prevents dispersed or deflected light from striking screen line areasprojected on the sensitized surface. This deflected or dispersed lightresults in a light fog in the line areas on a screen positive made withprimary screen H only, unless unusual skill is exercised in printing thescreen positive on the carbon resist.

To assure proper optical relationship or register of the objective orprimary and secondary screens H and 75, the two screens are preferablypermanently fastened together after the rulings, spacing, and properoptical relationship have been established for a given camera. This maybe accomplished for example by ruling the primary and secondary screensin register on opposite sides of a glass plate of proper thickness, orby utilizing separate screens that are brought into register andproperly spaced in a holding frame and then looked permanently in place,or by setting the screens in register and properly spaced in a suitabletransparent plastic.

In addition to the usual types of half tone ruled glass screens, Icontemplate the use of metallic screens which may be formed with properopening and line ratios for example by electro-deposition of nickel onmaster plates of the character described in United States Patent No.2,024,086 having the desired screen patterns. Such metallic screens havethe advantage that they reduce light diffraction to a minimum.

A full tone negative of the subject placed on plate 54 (Figure 11) willbe properly focused on the sensitized plate or film 14, and the screenor screens in place in frame 63, the first short exposure is made withthe stop 16 of Figure 13 in frame 6!. Stop 16 is provided with asubstantially square central opening 11 and is positioned in frame '62so that the sides of opening 1'! are parallel to the sides of the screensquares. Extending diagonally from the corners of opening 11 arerectangular openings 18 which preferably extend to the full capacity ofthe lens assembly, and are proportioned and arranged with respect to thescreen openings so that the light transmitted therethrough increases thelight passing through the corner areas of the screen squares to thesensitized surface. With a soft tone com mercial plate, by way ofexample-with a girls head and tone wedge as the subject, I have madethis exposure about six seconds. The dot formation as a result of suchan exposure above, when developed, has the general appearance of theformation illustrated in enlarged form in Figure 19, having a squarefull scale screen outlined with the density of exposure increasing fromthe periphery to the center of the dot.

After the first exposure stop 16 isreplaced with Y a second stop 19; andgiven'a second short exposure. This stop preferably is provided with afour pointed opening 80, provided with four pointed arms 8| which extenddiagonally a distance from the center of the opening equal to thedistance of the outer edges of extensions 18 from the center of theopening ll of stop 16. The maximum diagonal dimension of the openings inthese two stops are made equal, and the points-of openings 8| arepositioned in frame 52 so they-will coincide with the position assumedby the centers of extensions 18 of stop 16 during the first exposure.This places the diagonal axes of points 8| across the corners of thescreen squares, and the stop size is such that there will be no need tomake any change in screen distance for the second exposure.

The second exposure is then adding its effects to the first exposure. Inthe second exposure, which, in the specific example given in connectionwith the first exposure, was l'seconds, the

erally of the form illustrated in enlarged form in Figure 21.

After the second exposure has been completed a third exposure ispreferably made to increase the extent of exposure of thecentral coreareas of the dots preferably with stop 82 such as illustrated in Figure15, which is provided with a small central pin-hold opening 83. In thisexposure, which in the specific example given in connection with stopsl6 and 19 was about 90 seconds, the central core exposure of thepreviously formed dot exposures'isintensified further. The thirdexposure pattern when made with stop 82 alone and developed, is of thegeneral form illustrated in enlarged form in Figure 20.

After the foregoing exposures are completed theplate 'or film isdeveloped, and the resulting screen positive of the subject will be madeup of dots of varyingsizes, densities and tonal values depending uponthe tonal values of the subject as illustrated in enlarged form inFigures 9 and 10. The tonal values extend over the tonal range ofregular rotogravure positive, and each dot has thegeneral patternillustrated in enlarged form in Figure 18.

Because of its nature, no corrections can be made in my improved screenpositive. All corrections must be made in the negatives. However, by theprovision of my improved camera in which the proper lens, stop, screenand plate or film relationships and optical registry are all built intoeach camera for the production of a particular size and type ofnegative, without any provision for adjustment of anykind except theangular relation of dot position to the negative image, standardizedprocedures and formulae informulae and procedures which result inuniformly highgrade etching high grade prints with minimum skill inproduction.

In etching with my improved screen positive the image is printed on thesensitized 'resist by asingle'exposure and the resist is thentransferred to the plate'or cylinder-and the usual rotogravure etchingprocedure is followed. The etching .period usingmy improved screenpositive is about from twenty-three to twenty-five minutes givingcontrol of the etching approximately equal to that secured in theregular rotogravure etching. The

resulting etching consists of varying size and tone wells havingV-shaped cross-sections 45, 46, 41

and 48 such for example as are illustrated in fore intended to beembraced therein.

What is claimedand desired to be secured by United States LettersPatentis:

.1. The method of forming a screen positive from a sensitized softemulsion surface adapted for etching an intaglio printing form embodyingwells of V-shaped section which comprises the steps of making acontinuous tone negative of the subject; placing a first screen atapproximately half-tone distance from said surface; placing a secondscreen in contact with said surface in optical register with said firstscreen, said second screen having the same linage as said first screenbut having a smaller ratio of opaque to transparent areas; subjectingsaid surface to a plurality of successive exposures with a light imagefrom said negative through said screens and through a series ofdifferent stops, three of said stops having, respectively, asubstantially rectangular opening having extended corners, asubstantially cross-shaped opening and a relatively small circularopening, said openings being oriented with respect to said screens toform the outlines, accentuate the corners, and form central cores inseparated square distinct exposed dot like areas in gravure arrangementon said surface, with each dot having a central core of maximum exposureand gradually decreasing exposure from said core to its periphery; anddeveloping the thus exposed surface to produce thereon a positive imageof thesubject made up of transparent areas and distinct separated dotsof varying density.

2. As an article of manufacture, a screen positive produced inaccordance with the method of claim 1.

3. A method of forming a screen positive adapted for etching aninta-glio printing form embodying wells of V-shaped section whichcomprises the steps of subjecting a sensitized soft emulsion surface toa plurality of successive exposures of a continuous tone negative, eachexposure being made through both a primary screen at approximatelyhalf-tone distance from said surface and through a secondary screen incontact with said surface and in optical register with said primaryscreen, said secondary screen having the same linage as said primaryscreen but having a smaller ratio of opaque to transparent areas; eachexposure being made through a different stop, three of said stopshaving, respectively, a substantially rectangular opening havingextended corners, a substantially cross-shaped opening and a relativelysmall central opening, said openings being oriented with respect to saidscreen to form the outlines, accentuate the diagonals and corners,- andform central cores in separated square distinct exposed dot like areasin gravure arrangement on said surface, with each dot having a centralcore of maximum exposure and gradually decreasing exposure from saidcore to its periphery; and developing the thus exposed surface toproduce thereon a positive image of the subject made up of transparentareas and distinct separate dots of varying density.

4. As an article of manufacture, a screen positive produced inaccordance with the method of claim 3.

LUCIEN C. AUSTIN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,452,077 Huebner Apr. 17, 19231,562,757 Hammond Nov. 24, 1925 1,773,887 Stirling Aug. 26, 19301,849,036 Ernst Mar. 8, 1932 1,909,939 Ernst May 23, 1933 1,991,888Ernst Feb. 19, 1935 14 Number Name Date 2,010,042 Stirling Aug. 6, 19352,024,086 Ballard Dec. 10, 1935 2,039,195 Stirling Apr. 28, 19362,040,247 Dultgen May 12, 1936 2,048,876 Marx July 28, 1936 2,148,519Wilkinson Feb. 28, 1939 2,226,086 Wilkinson Dec. 24, 1940 2,282,337 Micset a1 May 12, 1942 2,376,596 Huggins May 22, 1945 2,387,048 Alger Oct.16, 1945 2,446,193 Rice Aug. 3, 1948 2,480,400 Dultgen Aug. 1949 FOREIGNPATENTS Number Country Date 686,763 France Apr. 15. 1930 711,572 GermanyFeb. 11, 1943 OTHER REFERENCES Smith, Other Uses of Half-Tone. BritishJournal of Photography, March 22, 1940, pages and 136 cited.

Mertle, Half-Tone Stops, American Photoengraver, September 1929, pages937 to 951, pages 938 and 942 cited.

